Some years ago I woke up early because of a loud aircraft flying over. Couldn’t get back to sleep and decided to use these precious early hours to visualize the air traffic around Hilversum. Every aircraft is equipped with a device called a transponder that transmits flight data about the flight into the air. Organizations like OpenSky aggregate these data and make them available. Below a screenshot of the result.

But when revisiting this project, I felt there were more opportunities. I obtained air traffic above the Netherlands from February to April (monday's only), resulting in 11 full days of traffic. Below a first visualisation. On mobile you can also see city names when zooming in. Bright white means much traffic passes by.

You can clearly see that Amsterdam is the hotspot of all the traffic. Let's see if there are more interesting patterns and visualisations. I won't plot the map anymore because the graphs are rendered better without.

Let's first split the traffic by altitude. If you watch this post on a computer, I recommend zooming in with ctrl+mousewheel.

Red: All the low traffic. Airfields such as Eelde, Eindhoven, Dusseldorf and Brussels are visible.
Blue: All the complex movements of traffic in and out of Amsterdam. These are standard routes being flown to keep the traffic manageable, so called STARs and SIDs.
Green: Aircraft passing over in mostly straight tracks.

There are more properties in the data, such as altitude, vertical speed and velocity. I've used different colormaps for aestetic purposes :)

Left: all the arriving flights are red and departures are blue.
Middle: This disco shows aircraft climbing or descending. The colormap is increasing with 1000m per color, starting from red for 0-1000m. Compare it with the top left graph: departing flights are quickly climbing to purple, whereas arrivals are flying lower longer. The green to yellow transitions indicate the points where arrival flights are converging for their approach.
Right: the average speed of the aircraft. Also here you see arrival routes are darker (slower) than departures.

And because COVID-19 is here, let's plot the data of the past weeks.

'Normally' there are 2700 flights above the Netherlands (including some North Sea) with a total airtime of 840 hours. That is the equivalent of about 35 aircraft flying continuously. The graph shows the dramatic slowdown to about 1/8 of the original volume.

The firelike image on the left side is slowly turning into a collection of night flies: the slowdown of traffic can be easily seen. This has been analyzed more extensively here.

I also went through callsigns that occur most often. Turns out there are some interesting patterns. Let's make it into a quiz: which pattern belongs to:

The coastguard
Aerial photography
Military flights
Emergency care flights (trauma)
Police helicopters
Commercial helicopter flights

Answers on the bottom of the post.

Let's end with some visualisations with a certain shade of blue. What type of flights do they represent?

That's it, I hope you like it!

Answers to the above:

A = Police helicopters. Interesting patterns! To the east the German police helicopter (callsign HUMMEL)
B = Aerial photography. To do their job, these flights often have dense tracks
C = Emergency medical flights. With callsign LIFELN (lifeliner), these helicopters are stationed in Amsterdam, Groningen, Rotterdam and Eindhoven.
D = Commercial helicopter flights. They mostly start from airfied Den Helder, flying personell to offshore rigs
E = Coast Guard, with callsign NCG
F = Military. In april a NATO flight departed from NATO Air Base Geilenkirchen with a Boeing E-3 Sentry

And the blues represent our flagship carrier KLM! If you want you can download the higher resolution images

Tip: Thanks to OpenSky, Datashader and some wonderful tutorials on the internet, e.g. US Census and PyViz. Used code from these examples as well.

Note: Here you can find my other posts